logic gate

You’ve seen CMOS logic, you’ve seen diode-resistor logic, you’ve seen logic based on relays, and some of you who can actually read have heard about rod logic. [Julian] has just invented optoisolator logic. He has proposed two reasons why this hasn’t been done before: either [Julian] is exceedingly clever, or optoisolator logic is a very stupid idea. It might just be the former.

Inside each optoisolator is a LED and a phototransistor. There’s no electrical connection between the two devices, which is exactly what you need in something that’s called an isolator. [Julian] was playing around with some optoisolators one day to create a weird push-pull circuit; the emitter of one phototransistor was connected to the collector of another. Tying the other ends of the phototransistor to +5V and Gnd meant he could switch between VCC and VDD, with every other part of the circuit isolated. This idea whirled around his mind for a few months until he got the idea of connecting even more LEDs to the inputs of the optoisolators. He could then connect the inputs of the isolators to +5V and Gnd because of the voltage drop of four LEDs.

A few more wheels turned in [Julian]’s head, and he decided to connect a switch between the two optoisolators. Connecting the ‘input’ of the circuit to ground made the LED connected to +5V light up. Connecting the input of the circuit to +5 made the LED connected to ground light up. And deeper down the rabbit hole goes [Julian].

With a few more buttons and LEDs, [Julian] created something that is either an AND, NAND, OR NOR, depending on your point of view. He already has an inverter and a few dozen more optoisolators coming from China.

It is theoretically possible to build something that could be called a computer with this, but that would do the unique properties of this circuit a disservice. In addition to a basic “1” and “0” logic state, these gates can also be configured for a tri-state input and output. This is huge; there are only two universal gates when you’re only dealing with 1s and 0s. There are about 20 universal logic gates if you can deal with a two.

Here is a very nice project that [Znaxque] finished a few months ago: a simple nixie clock made with logic gates only. In this build, the mains 50Hz is used as a time base instead of a 32KHz crystal that most readers here may use. In the very long term, this clock may actually be more precise than a crystal-based one as power companies in Europe adjust the mains frequency. However, at a given moment the difference between this clock and a reference may be as big as 60 seconds.

The design was sketched on a simple piece of paper and later made using salvaged ICs. [Znaxque] only bought the six IN-14 nixies for $45 and the veroboard shown in the picture above. The BCD to Decimal decoders are 74141s and three buttons are present on the board to set minutes, hours, as well as resetting all the counters.

Building logic gates out of silicon is old hat, as is building them from discrete transistors, 555 chips, LEGO, and even gears. [Yukio-Pegio Gunji] and [Yuta Nishiyama] from Kobe University, along with [Andrew Adamatzky] from the aptly named Unconventional Computing Centre at the University of the West of England decided they needed a new way to build logic gates using crabs (PDF warning). Yes, the team successfully built functional logic gates using Mictyris guinotae, a species of soldier crab native to the South Seas.

The colonies of soldier crabs that inhabit the lagoons of Pacific atolls display a unique swarming behavior in their native habitat. When in a swarm of hundreds of individuals, the front of the swarm is driven by random turbulence in the group, while the back end of the swarm simply follows the leaders. Somehow, this is a successful evolutionary strategy, but it can also be exploited to build logic gates using only crabs.

The team constructed a Y-shaped maze for a pair of crabs to act as an OR gate. When two soldier crabs are placed at the top of the ‘Y’, they move forward until they meet and exit the maze through the output. This idea can be expanded to a slightly more complex AND gate, functionally identical to the electron-powered AND gate in a 7408 logic chip.

While the team has only made OR and AND gates – nothing functionally complete yet – there’s no reason to believe this crab-based system of computation couldn’t be expanded to a (very) basic calculator.